diff --git a/src/storage/expressions/Variable.cpp b/src/storage/expressions/Variable.cpp
index b0acaba22..492a6ae32 100644
--- a/src/storage/expressions/Variable.cpp
+++ b/src/storage/expressions/Variable.cpp
@@ -51,14 +51,4 @@ namespace storm {
             return this->getType().isNumericalType();
         }
     }
-}
-
-namespace std {
-    std::size_t hash<storm::expressions::Variable>::operator()(storm::expressions::Variable const& variable) const {
-        return std::hash<uint_fast64_t>()(variable.getIndex());
-    }
-    
-    std::size_t less<storm::expressions::Variable>::operator()(storm::expressions::Variable const& variable1, storm::expressions::Variable const& variable2) const {
-        return variable1.getIndex() < variable2.getIndex();
-    }
-}
+}
\ No newline at end of file
diff --git a/src/storage/expressions/Variable.h b/src/storage/expressions/Variable.h
index e99fd70c4..8bb7e0ce8 100644
--- a/src/storage/expressions/Variable.h
+++ b/src/storage/expressions/Variable.h
@@ -8,26 +8,6 @@
 #include "src/storage/expressions/Type.h"
 #include "src/storage/expressions/Expression.h"
 
-namespace storm {
-    namespace expressions {
-        class Variable;
-    }
-}
-
-namespace std {
-    // Provide a hashing operator, so we can put variables in unordered collections.
-    template <>
-    struct hash<storm::expressions::Variable> {
-        std::size_t operator()(storm::expressions::Variable const& variable) const;
-    };
-    
-    // Provide a less operator, so we can put variables in ordered collections.
-    template <>
-    struct less<storm::expressions::Variable> {
-        std::size_t operator()(storm::expressions::Variable const& variable1, storm::expressions::Variable const& variable2) const;
-    };
-}
-
 namespace storm {
     namespace expressions {
         class ExpressionManager;
@@ -141,4 +121,22 @@ namespace storm {
     }
 }
 
+namespace std {
+    // Provide a hashing operator, so we can put variables in unordered collections.
+    template <>
+    struct hash<storm::expressions::Variable> {
+        std::size_t operator()(storm::expressions::Variable const& variable) const {
+            return std::hash<uint_fast64_t>()(variable.getIndex());
+        }
+    };
+    
+    // Provide a less operator, so we can put variables in ordered collections.
+    template <>
+    struct less<storm::expressions::Variable> {
+        std::size_t operator()(storm::expressions::Variable const& variable1, storm::expressions::Variable const& variable2) const {
+            return variable1.getIndex() < variable2.getIndex();
+        }
+    };
+}
+
 #endif /* STORM_STORAGE_EXPRESSIONS_VARIABLE_H_ */
\ No newline at end of file